1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device and, particularly, to a method of forming an electrode wiring on a silicon substrate through a barrier metal.
2. Description of the Prior Art
Heretofore, aluminum (Al) or an alloy thereof has been mainly used as material for forming electrode wirings which are in ohmic contact with respective impurity diffusion regions formed in a silicon (Si) substrate and further with the silicon substrate itself. As well known in the art, if such a metal for electrode wiring is directly formed on the silicon substrate, an alloy spike and/or silicon nodule may be produced by reaction between aluminum and silicon due to thermal hysteresis of the metal deposition step and subsequent steps. In a case of a single layer wiring of aluminum or its alloy, breakage of wiring due to electromigration and/or stressmigration becomes a severe problem. In order to prevent aluminum and silicon in contact regions from reacting with each other, it is usual to form a barrier metal layer between the silicon substrate and the metal layer forming the electrode wiring. A multi-layer wiring using such barrier metal layer is effective in preventing such wiring breakage due to electromigration or stressmigration.
The barrier metal layer is generally formed only on the contact regions of the impurity diffusion regions to the electrodes. In order to improve the durability against stressmigration, however, it is popular recently that the barrier metal layer is formed not only on the contact regions but also on a wiring formation regions beneath the electrode wirings. The latter scheme is becoming popular. As the barrier metal to be formed beneath the electrode wiring, a titanium (Ti) film or a titanium nitride (TiN) film is mainly used.
More specifically, an interlayer insulating film of such as silicon dioxide is formed on a silicon substrate in which desired diffusion regions are formed through desired impurity diffusion steps. After a contact hole is formed in the interlayer insulating film, a titanium (Ti) film and a titanium nitride (TiN) film are formed sequentially on the surface of the silicon substrate as a barrier metal, followed by carrying out heat treatment. An aluminum (Al) film is thereafter formed on the barrier metal layer, and these three metal layers are then patterned to form a three-layer electrode wiring.
The titanium nitride film as the barrier metal is usually formed by reactive sputtering with using titanium as a target electrode in a mixture gas of argon (Ar) and nitrogen gas (N.sub.2) as sputtering atmosphere. The subsequent heat treatment is performed by lamp annealing within nitrogen gas or NH.sub.3 gas. By this heat treatment, the titanium film within the contact hole is silicided from the side of the silicon substrate while non-reacted titanium of the titanium nitride film and the titanium film are nitrided from the side of the sputtering gas. Therefore, the performance of the titanium film and the titanium nitride film as the barrier metal is improved and the contact resistance is reduced. This heat treatment was reported by H. Joswig and W. Pamler in Jun. 12-13, 1990, VMIC Conference.
However, in the fabrication method of semiconductor device, mentioned above, when the titanium nitride film is lamp-annealed to improve the properties thereof, it is crystallized by rapid heating and shrinked, resulting in fine cracks in the titanium nitride film. Therefore, the barrier performance of the titanium nitride film is degraded and leakage current is increased, resulting in degradation of reliability of the semiconductor device.